1. Field of the Invention
This invention relates to a high-solids polyurethane film-forming composition of a polyisocyanate and low molecular weight polyester and addition polymers that have controlled hydroxylfunctionality.
2. Description of the Prior Art
Polyurethane compositions have generally been used as coatings, adhesives, or molding materials. The inclusion in these compositions of a hydroxyl-containing polymer and a polyisocyanate is shown, for example, in U.S. Pat. No. 3,245,941 issued Apr. 12, 1961 to Mayer, et al. Such compositions are useful as coatings, but do not provide the durability, flexibility, and chemical resistance required for industrial finishes.
Polyurethane coatings which consist of hydroxyl-containing acrylic polymers and hydroxylfunctional polyesters that are crosslinked with a polyisocyanate are shown, for example, in U.S. Pat. No. 4,020,216 issued Apr. 26, 1977 to Miller and in U.S. Pat. No. 3,919,351 issued Nov. 11, 1975 to Chang, et al. These coatings exhibit the above-mentioned properties necessary in industrial finishes, but cannot be usefully applied at highsolids levels.
With the current emphasis on reduction of solvent emissions and lowering of energy consumption, there is a continued need for a polyurethane coating which not only can be spray-applied at high weight-solids levels but also can be cured at ambient temperature to produce a durable, flexible, chemical-resistant finish.